The world got a front-row view of the rite of baptism this past week as Archbishop of Canterbury Justin Welby christened Prince George, a future king of England.

Welby made it a teachable moment for a country where only one in six are baptized. In a YouTube video, he explains that by bringing their son forward for baptism, Prince William and Duchess Catherine of Cambridge are "bringing God into the middle of it all."

Last month, Pope Francis gave the sacrament a boost when he called a pregnant, unmarried woman to encourage her faith and offered to baptize her baby, a reminder to Catholics that children of unmarried parents are welcome in the church.

Yet, these leading voices in Christendom are driving against a current of declining baptism rates in the United States. Though no single entity tracks all baptisms of U.S. Christians, the numbers available reflect a marked drop. (Though it's notable that a growing number of U.S. Christians belong to vast non-denominational megachurches, independent entities reporting to no one.) Experts point to:

A rise in secularism: Set aside that one in five Americans today say they have no religious identity. Even among those who do claim a denominational label, "there is a de-emphasis on practicing faith," said the Rev. Frank Page, president of the Southern Baptist Convention's Executive Committee.

"People want God but they're not happy with churches," he said, so rites such as baptism are victims of an "anti-denominational, anti-institutional, even anti-church era."

The SBC, which considers baptism a key marker of Christian faith and also denominational vitality, tallied 314,959 baptisms in 2012 — a low not seen since 1948 even as the total number of members of the Southern Baptist Convention has more than doubled.

"It's a sad situation," said Thom Rainer, president of LifeWay Christian Resources. "In 1948 we had 6 million members of the SBC but today we have (nearly) 16 million members."

Yet, Rainer called himself an "obnoxious optimist." Although his research on the nation's 80 million Millennials (born between 1980 and 2000) shows that only 15% call themselves Christian, Rainer said those youth are "on fire" for faith.

"So it all might turn around," he said. "I'm standing on prayerful hope."

More interfaith marriages: One in four U.S. households were multifaith in 2006, up from 15% in 1988, says Naomi Schaefer Riley in her book, 'Til Faith Do Us Part. Such couples often compromise by ditching specific faith rituals such as baptism to avoid contention.

Even so, divorce is three times more prevalent in interfaith families with children than in same-faith households, often leaving the children of those marriages confused or indifferent about God, sacraments or the path to salvation.

Fewer marriages officiated by clergy: When a couple opts not to get married in a church, it's an early sign that a couple might view the blessings of faith as optional for their family, said Mark Gray, senior research associate at Georgetown University's Center for Applied Research in the Apostolate.

Gray tied the sliding baptism rate to the decline in marriages officiated by a priest. The Catholic Church regards marriage as a sacrament to be celebrated in the sacred space of a church.

There's a disconnect at the get-go "if you are getting married at a country club or the beach," said Gray. "If you haven't been married in a church, you may be less likely to present your child for baptism."

In 1970, 426,000 marriages occurred in U.S. Catholic churches — a full 20% of all U.S. marriages that year. By contrast, in 2011, there were 164,000 such weddings — only 8% of all marriages. But in both years, Catholics comprised 23% of the U.S. population.

Catholic baptism rates fell at a parallel pace — from just more than 1 million baptisms in 1970 down to 793,103 baptisms in 2011.

Misunderstandings: Gray said the rising number of out-of-wedlock births may contribute to the decline in baptisms. "Single parents may be less apt to bring a child for baptism because of a misapprehension that they won't be welcome." But as the pope's call to the Italian woman shows, "the church is not going to turn you away," Gray said.

The Rev. James Martin, a Jesuit priest, author and editor at large at America magazine, worried that many parents don't understand the theology of baptism, "the most familiar but misunderstood sacrament."

"It's become a rite of passage for the family rather than what it really means — an incorporation into the Christian community. So some parents don't realize why it takes place during a Mass or why godparents should be Catholics. They are surprised that preparation is involved."

Even so, said Martin, "It's my favorite sacrament, much more than weddings. Everyone is happy at a baptism. No one is worried about the flowers or the reception or what the baby is wearing. It's a great teachable moment about the church, God and love."